1. Field of the Invention
The present invention relates to a carburetor for internal combustion engines and, more particularly, to a carburetor in which the flow of the vapor evaporated from a liquid fuel in the float chamber is suitably controlled to prevent loss of fuel and environmental contamination.
2. Description of the Prior Art
A typical conventional carburetor for internal combustion engines, which is designed to control the flow of fuel vapor filling the space on the free surface of liquid fuel in a float chamber, includes an inner vent passage through which the space in the float chamber is communicated with the intake passage of the carburetor, an outer vent passage through which the space in the float chamber is communicated with a vessel for storing the fuel vapor such as a charcoal canister, and a solenoid valve adapted to open and close the outer vent passage as its coil is energized and de-energized in accordance with the operation of engine ignition key. In this conventional carburetor, since the inner vent passage is always opened, a part of the fuel vapor is inconveniently relieved or discharged to the intake passage during the engine-off period, resulting in a contamination of the air cleaner and starting failure of the engine. In addition, it is impossible to absorb all of the fuel vapor in the charcoal canister during the engine-off period, because a considerable part of the evaporated fuel is relieved to the intake passage.
To avoid such drawbacks, there has been proposed a carburetor having a valve adapted to operate in response to the vacuum in the intake passage, in such a manner that it normally closes and opens the inner and outer vent passages, respectively, and opens and closes the inner and outer vent passages, respectively, when a vacuum is generated in the intake passage. In this carburetor, however, the inner and outer vent passages are inconveniently closed and opened, respectively, when the vacuum in the intake passage has become low during running operation of engine so that the function of the inner vent passage is failed.